The present invention relates to sealing systems, and more particularly, to seal ring backup devices having a scarf cut and methods of use thereof.
Preventing leakage of fluids such as liquids and gasses between sliding or turning parts of a machine often requires a sealing system that includes at least a seal ring, a seal ring backup device, and a gland designed to receive the seal ring and seal ring backup device. Common examples of seal rings and seal ring backup devices include an o-ring and an o-ring backup device, which are configured to fit into a gland. A gland may be part of a body such as a bore or a movable part such as a piston. As used herein, a “gland” is a machined cavity including a machined groove and mating surfaces into which a seal ring and/or a seal ring backup device are fitted. Within a gland, a seal ring may close the gap between mating parts, allowing a seal to form. A gland is usually made in a portion of metal or another rigid material. In order to form a proper seal, the design characteristics of a gland (e.g., diameter, removable parts, contour of the cavity walls, etc.) must be compatible with the specific design considerations of the seal ring and the seal-ring backup device.
In particular, o-rings are torus, or doughnut-shaped seal rings used to provide a deformable seal for mating parts that may have gaps, among many things, due to parts fit or dimensional tolerances between parts. O-rings are usually molded from elastomers such as deformable rubber and can be found installed on the high pressure side (fluids generally flow from high pressure to low pressure) of a variety of sealed systems including valves, pump shafts, and hydraulic pistons. O-ring backup devices are ring-shaped protective elements used to support the o-rings against mechanical failure (e.g., resulting from extreme deformation) and enhance the pressure rating of an o-ring seal. O-ring backup devices are typically made from relatively rigid materials and installed on the lower pressure side.
While an o-ring's primary function is to provide a seal, an o-ring backup device does not typically have any intended sealing function. Instead, an o-ring backup device is designed to remove extrusion gaps inside a gland. As used herein, “extrusion” generally refers to an extreme case of deformation where a small portion of a seal ring is forced into a small clearance gap within a cavity. As used herein, “clearance gap” generally refers to the gap between two mating surfaces. Extrusion can often lead to physical damage to a seal ring, which leads to seal failure. An o-ring backup device, by way of its design, can reduce or prevent extrusion of the o-ring by effectively closing the clearance gap within the cavity. Thus, an o-ring backup device can prolong the life span of an o-ring within a sealing system and ensure a properly working seal. Seal system pressure ratings can also be significantly increased when seal ring backup devices are used.
In a typical setup, an o-ring may be installed in a sealing system generally featuring a cylindrical surface, such as a piston and cylinder combination, a piston rod and rod guide combination, or a rotating shaft and housing combination. The gland may be machined in an exterior surface of the piston or, alternatively, in an interior surface of the cylinder (sometimes referred to as “the bore”). A proper installation requires that the o-ring fits into the gland and firmly contacts the side walls of the mating surfaces. Elevated temperatures and pressures can impose severe burden on the physical and mechanical properties of an elastomeric o-ring, increasing the tendency for extrusion. A variety of factors can cause extrusion in o-rings including, but not limited to, excessive clearances, o-ring material being too soft, improper machining of the o-ring gland, and improper size of the o-ring.
In order to prevent extrusion of the o-ring, an o-ring backup device may be installed into the gland to contact the o-ring from the low pressure side. Incoming pressure can act on the o-ring backup device, which, in turn, can expand or move too close and essentially eliminate the clearance gap within the gland cavity. This ensures that an o-ring will not extrude into the clearance gap.
While a seal ring backup device is useful and can allow softer elastomers to be used in higher pressure and temperature settings, it may not be useful in all types of glands. For example, an open gland has removable parts that allow a seal ring backup device to easily fit into a gland cavity but, currently, it is believed that there is no known wedge type seal system that can be used in a “blind” gland. Blind gland is also referred to as a closed gland and cannot be taken apart. Extra stretch of the seal ring and seal ring backup device may be necessary when using a blind gland. Thus, a blind gland requires additional design considerations as the inner diameter of the seal ring backup device is smaller than the outer diameter of a gland into which it must fit.